Enhanced self-reported affect and prosocial behaviour without differential physiological responses in mirror-sensory synesthesia Kalliopi Ioumpaa,b,*, Sarah A. Grahamc, Tommy Clausnera, Simon E. Fisher a,c, Rob van Liera, Tessa M. van Leeuwena,* a Radboud University, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, the Netherlands b Netherlands Institute for Neuroscience, Royal Netherlands Academy for Arts and Sciences, Amsterdam, the Netherlands c Language and Genetics Department, Max Planck Institute for Psycholinguistics, Nijmegen, the Netherlands Accepted for publication in Philosophical Transactions of the Royal Society B * Corresponding authors: Kalliopi Ioumpa (
[email protected]) Tessa M. van Leeuwen (
[email protected]) 1 Abstract Mirror-sensory synesthetes mirror the pain or touch that they observe in other people on their own bodies. This type of synesthesia has been associated with enhanced empathy. We investigated whether the enhanced empathy of people with mirror-sensory synesthesia influences experience of situations involving touch or pain, and whether it affects their prosocial decision making. Mirror-sensory synesthetes (N=18, all female), verified with a touch-interference paradigm, were compared to a similar number of age-matched control individuals (all female). Participants viewed arousing images depicting pain or touch; we recorded subjective valence and arousal ratings, and physiological responses, hypothesizing more extreme reactions in synesthetes. The subjective impact of positive and negative images was stronger in synesthetes than in control participants; the stronger the reported synesthesia, the more extreme the picture ratings. However, there was no evidence for differential physiological or hormonal responses to arousing pictures. Prosocial decision making was assessed with an economic game assessing altruism, in which participants had to divide money between themselves and a second player.